When backpriming T&G solid sawn wood, is it best to prime the tongues
and grooves, or not? On the one hand, sealing all sides is good; on
the other, it would be easy to get excess paint in the corners which
could interfere with the mating of the T&G. But the groove is
typically 1/16" wider than the tongue, so perhaps that's not really an
My father always objected to back priming when the back would not be
subject to moisture. Wood likes to breath. There will always be some
moisture penetrating the finished side, If everything is sealed it tends to
come out wherever and that might mean the finished side and it may will take
the finish with it.
A couple comments:
I believe that latex paint is more vapor permeable than oil base
paint. So perhaps the analysis above only applies to oil based
Also, the main argument for finishing both faces is that otherwise the
differential rates of moisture movement through the two faces when the
wood is exposed to a shift in ambient humidity could lead to
differential rates of expansion/contraction, i.e. cupping. If the
wood is unrestrained then this cupping should be transient, but if it
is restrained then compression set on one side could make the cupping
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